In the world of business, bad news often surfaces serially: You see a cockroach in your kitchen; as the days go by, you meet his relatives.

That nugget from Warren Buffett came to mind Tuesday as shares of Signet Jewelers, operator of Jared, Kay and Zales jewelry stores, plummeted. The drop followed disclosures, initially by The Washington Post, of an explosive sexual discrimination case filed by a group of the company’s former employees.